/*
 * CompositeValue.java July 2007
 *
 * Copyright (C) 2007, Niall Gallagher <niallg@users.sf.net>
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * permissions and limitations under the License.
 */

package wx.xml.simpleframework.xml.core;

import wx.xml.simpleframework.xml.strategy.Type;
import wx.xml.simpleframework.xml.stream.InputNode;
import wx.xml.simpleframework.xml.stream.OutputNode;
import wx.xml.simpleframework.xml.stream.Style;

/**
 * The <code>CompositeValue</code> object is used to convert an object
 * to an from an XML element. This accepts only composite objects and
 * will maintain all references within the object using the cycle
 * strategy if required. This also ensures that should the value to
 * be written to the XML element be null that nothing is written.
 *
 * @author Niall Gallagher
 * @see wx.xml.simpleframework.xml.ElementMap
 */
class CompositeValue implements Converter {

    /**
     * This is the context used to support the serialization process.
     */
    private final Context context;

    /**
     * This is the traverser used to read and write the value with.
     */
    private final Traverser root;

    /**
     * This is the style used to style the names used for the XML.
     */
    private final Style style;

    /**
     * This is the entry object used to provide configuration details.
     */
    private final Entry entry;

    /**
     * This represents the type of object the value is written as.
     */
    private final Type type;

    /**
     * Constructor for the <code>CompositeValue</code> object. This
     * will create an object capable of reading an writing composite
     * values from an XML element. This also allows a parent element
     * to be created to wrap the key object if desired.
     *
     * @param context this is the root context for the serialization
     * @param entry   this is the entry object used for configuration
     * @param type    this is the type of object the value represents
     */
    public CompositeValue(Context context, Entry entry, Type type) throws Exception {
        this.root = new Traverser(context);
        this.style = context.getStyle();
        this.context = context;
        this.entry = entry;
        this.type = type;
    }

    /**
     * This method is used to read the value object from the node. The
     * value read from the node is resolved using the template filter.
     * If the value data can not be found according to the annotation
     * attributes then null is assumed and returned.
     *
     * @param node this is the node to read the value object from
     * @return this returns the value deserialized from the node
     */
    public Object read(InputNode node) throws Exception {
        InputNode next   = node.getNext();
        Class     expect = type.getType();

        if (next == null) {
            return null;
        }
        if (next.isEmpty()) {
            return null;
        }
        return root.read(next, expect);
    }

    /**
     * This method is used to read the value object from the node. The
     * value read from the node is resolved using the template filter.
     * If the value data can not be found according to the annotation
     * attributes then null is assumed and returned.
     *
     * @param node  this is the node to read the value object from
     * @param value this is the value to deserialize in to
     * @return this returns the value deserialized from the node
     * @throws Exception if value is not null an exception is thrown
     */
    public Object read(InputNode node, Object value) throws Exception {
        Class expect = type.getType();

        if (value != null) {
            throw new PersistenceException(node, "Can not read value of %s for %s", expect, entry);
        }
        return read(node);
    }

    /**
     * This method is used to read the value object from the node. The
     * value read from the node is resolved using the template filter.
     * If the value data can not be found according to the annotation
     * attributes then null is assumed and the node is valid.
     *
     * @param node this is the node to read the value object from
     * @return this returns true if this represents a valid value
     */
    public boolean validate(InputNode node) throws Exception {
        Class  expect = type.getType();
        String name   = entry.getValue();

        if (name == null) {
            name = context.getName(expect);
        }
        return validate(node, name);
    }

    /**
     * This method is used to read the value object from the node. The
     * value read from the node is resolved using the template filter.
     * If the value data can not be found according to the annotation
     * attributes then null is assumed and the node is valid.
     *
     * @param node this is the node to read the value object from
     * @param key  this is the name of the value element
     * @return this returns true if this represents a valid value
     */
    private boolean validate(InputNode node, String key) throws Exception {
        String    name   = style.getElement(key);
        InputNode next   = node.getNext(name);
        Class     expect = type.getType();

        if (next == null) {
            return true;
        }
        if (next.isEmpty()) {
            return true;
        }
        return root.validate(next, expect);
    }

    /**
     * This method is used to write the value to the specified node.
     * The value written to the node must be a composite object and if
     * the object provided to this is null then nothing is written.
     *
     * @param node this is the node that the value is written to
     * @param item this is the item that is to be written
     */
    public void write(OutputNode node, Object item) throws Exception {
        Class  expect = type.getType();
        String key    = entry.getValue();

        if (key == null) {
            key = context.getName(expect);
        }
        String name = style.getElement(key);

        root.write(node, item, expect, name);
    }
}
